Biomechanics of the shoulder in youth baseball pitchers: implications for the development of proximal humeral epiphysiolysis and humeral retrotorsion.

Background: The effects of repetitive throwing on the shoulders of developing athletes are not well understood because of the paucity of data describing the biomechanics of youth pitchers and the plasticity of the developing skeleton.

Hypothesis: The direction and magnitude of the stresses that exist at the proximal humeral physis during the fastball pitching motion are consistent with the development of proximal humeral epiphysiolysis (Little League shoulder) and/or humeral retro-torsion.

Study Design: Descriptive laboratory study.